Uninterruptible power supplies (UPS's) have long been used to provide at least temporary auxiliary power to electronic devices. Typically, a UPS is configured to switch between a primary power source and a standby power source as necessary to maintain constant power to a load.
For example, the primary power source may be a utility power supply, and the standby power source may take the form of a battery system. The UPS will normally operate in a line mode in which the utility power signal is passed to the load when the utility power signal is within predefined parameters. In the line mode, the UPS will typically also charge the battery system. When the utility power falls outside of the predefined parameters, the UPS will switch to standby mode in which an AC signal is generated based on the energy stored in the battery system.
A battery system for use in a UPS is typically specified by the nature of the UPS system, a load voltage level required for proper operation of the load, and a length of time the UPS operates in standby mode. Commonly, a number of batteries are connected in series in a string to provide a desired battery voltage level necessary for generation of the load voltage level, and a number of strings are connected in parallel to increase the storage capacity of the battery system. Accordingly, it is not uncommon for a UPS system to be provided with two to four strings comprising three or four batteries each.
In line mode, the UPS system includes a charging system for generating a charge signal that is applied to the battery system to maintain a full charge on the batteries so that the battery system operates to specification when in standby mode.
An object of the present invention is to provide improved battery charge systems for strings of series connected batteries and methods in general and improved battery charge systems specifically designed for use on any battery charger as generally described above.